declination (n.)

late 14c., declinacioun, in astronomy, "distance of a heavenly body from the celestial equator, measured on a great circle passing through the body and the celestial pole," from Old French declinacion (Modern French déclinaison) and directly from Latin declinationem (nominative declinatio) "a bending from (something), a bending aside; the supposed slope of the earth toward the poles; a turning away from (something), an avoiding," noun of action from past-participle stem of declinare (see decline (v.)). From c. 1400 as "a bending or sloping downward." Related: Declinational.